Component with locally limmited reinforcement regions and method for production thereof

ABSTRACT

The invention relates to a component consisting of a high-strength sheet, in particular a structural component, which is provided with a deformation structure in a locally limited stiffening region, this deformation structure considerably increasing the local stiffness of the component compared with conventional components. The stiffness-increasing deformation structure consists of a periodic grid of concave and convex bulges nested one inside the other. It is embossed in certain, locally limited regions of the sheet by means of a deep-drawing method. The regular periodic grid structure of the stiffening pattern permits a computational simulation of the stiffnesses to be achieved and, as a consequence thereof, a systematic optimization of the stiffening structure for the respective component. The bulge depths may be locally varied inside the stiffening structure, as a result of which local variations in the stiffness of the component are specifically achieved inside the stiffening region.

[0001] The invention relates to a component consisting of ahigh-strength sheet which is provided with a stiffness-increasingdeformation structure in a locally limited stiffening region and to amethod of producing it.

[0002] Many components in automobile construction, in particularstructural components, must meet high demands with regard to bothstrength and stiffness. At the same time, there is considerable interestin realizing lightweight construction concepts in vehicle building andtherefore in reducing the weight of these parts as much as possible. Thedesired strength, with simultaneous reduction in weight, can be achievedif thin sheets made of high-tensile steels are used as the startingmaterial, these sheets having a strength comparable with thicker sheetsmade of conventional steels. However, these thinner sheets, in order toachieve the required stiffness, must be provided withstiffness-increasing structures, such as, for example, beads and/orstuds. Since high stiffness is only required in selected regions of thecomponents as a rule, whereas in other regions the stiffness is only ofsecondary importance, it is advantageous to provide thesestiffness-increasing structures only in those regions of the componentswhich are subjected to particular loads with regard to stiffness duringoperation.

[0003] The local stiffness increase of components made of sheet metalhas been disclosed by DE 297 12 622 U1 establishing the generic type. Inthis publication, it is proposed to provide the sheet-metal billets withwart-shaped studs in selected regions before the forming of thecomponent geometries, these wart-shaped studs being incorporated in thesheet-metal billets by means of an embossing method. Since the studstructure is largely lost during the subsequent shaping of the componentgeometry, e.g. by means of a drawing method, this stud stiffening issuitable mainly for those regions which are not formed or are not formedto an appreciable extent in the following forming process.

[0004] The production of a locally stiffness-increased componentaccording to DE 297 12 622 U1 therefore consists of two processsteps—namely the embossing of the sheet-metal billet with a studstructure followed by the forming of the sheet-metal billet to producethe component geometry—and is therefore relatively expensive.Furthermore, there is often the requirement to also provide inparticular the forming regions on the component withstiffness-increasing structures, which is not possible with the methodproposed in DE 297 12 622 U1. Finally, there is the requirement toachieve a greater local stiffness increase, in particular a greaterincrease in the flexural stiffness, which cannot be achieved with thestud structures shown in DE 297 12 622 U1.

[0005] DE 196 34 244 discloses a method for the stiffness-increasingtexturing of sheets, by means of which a sheet-metal billet is texturedwith bulges from both sides in several stages. In this case, periodicpatterns of large bulges are produced, in the hollows of which bulgessmall bulges form from the opposite side. Although this surfacestructure ensures very good compressive and flexural stiffness, thebulging method proposed for producing it can only be applied to verythin sheets and is therefore not suitable for the stiffness increase ofstructural components, e.g. for vehicle building. Furthermore, DE 196 34244 describes a bulging method by a continuous process in which theentire surface of a crude sheet is provided with bulges. Therefore, onthe one hand, no specific local stiffness increase of the crude sheet ispossible; on the other hand, the bulge structure and thus the stiffnessincrease achieved would be lost in a forming process following thebulging process.

[0006] The object of the invention is therefore to produce sheet-metalcomponents having specifically incorporated, spatially limitedstiffening regions which have a considerable increase in the localstiffness compared with conventional components provided with localstiffening regions. The object of the invention is also to propose asimple method of achieving such a local stiffness increase onsheet-metal components.

[0007] This object is achieved according to the invention by thefeatures of claims 1 and 3.

[0008] Accordingly, the surface of the component is provided in selectedregions with a stiffening structure which consists of a periodic grid ofconcave and convex bulges nested one inside the other. Such a stiffeningstructure ensures a considerable stiffness increase compared with thestuds and beads incorporated in a conventional manner. This relates bothto flexural and compressive stiffness and to stiffness against twisting.Furthermore, the regular periodic grid structure of the stiffeningpattern permits a computational simulation of the stiffnesses achievedin the process and, as a consequence thereof, a systematic optimizationof the stiffening structure for the respective component. The stiffeningstructure can be characterized by means of a few parameters (bulge radiiand depths, grid constant of the stiffening structure, and orientationof the grid direction relative to the component), so that the parametersrequired for a certain local stiffness can be determined at thepreliminary stages of the component production by means of a simulation.Furthermore, the bulge depths inside the stiffening structure can belocally varied, as a result of which specifically local variations inthe stiffness can be achieved inside the stiffening region.

[0009] A stiffening structure which is especially simple to simulate andwhich at the same time ensures a high stiffness in all spatialdirections is a pattern of bulges nested one inside the other on ahexagonal grid (see claim 2).

[0010] The stiffening structure is produced on the component by means ofa drawing method (see claim 3): when the press punch is lowered duringthe course of the drawing method, sufficiently high forces can beapplied in order to also provide sheets of high-tensile steel which areseveral millimeters thick with the above-described complex stiffeningstructures in a controlled manner in terms of the process. The methodcan therefore be applied to any desired sheets, as long as the sheetsare made of a material capable of being drawn.

[0011] It is especially favorable with regard to the production costs ofthe component if the shaping of the component geometry and theincorporation of the stiffening structure is effected in a singleoperation which essentially corresponds to a deep-drawing operation (seeclaim 4). In this case, the stiffening structure, which, depending onthe stiffening increase required, projects beyond the surroundingcomponent region by 2 to 4 mm, is formed in the sheet-metal part at thefinal pressure of the deep-drawing process. The high pressures occurringin the process produce an additional crystalline change in thesheet-metal structure, a factor which additionally contributes to thestiffness increase of the component. Furthermore, this incorporation ofthe stiffening structure during the shaping of the component geometrypermits the local stiffening of component surfaces having any desiredcurvature.

[0012] The invention is explained in more detail below with reference toan exemplary embodiment shown in the drawings, in which:

[0013]FIG. 1 shows a detail of a side sheet of a longitudinal memberwith a local stiffness-increasing deformation structure,

[0014]FIG. 2 shows a lateral section through a side sheet along sectionline II-II in FIG. 1,

[0015]FIG. 3 shows an alternative configuration of the deformationstructure,

[0016]FIG. 4 shows a schematic representation of a deep-drawing tool forproducing a side sheet for the longitudinal member in FIG. 1.

[0017]FIG. 1 shows a detail of a longitudinal member 1 which is made ofsteel sheet and forms part of a vehicle frame of a goods vehicle. Thelongitudinal member 1 consists of a plurality of individual parts 2produced by means of a deep-drawing method and contains in particular aside sheet 2′ which is connected to further individual parts (not shownin FIG. 1) of the longitudinal member 1 by welding. The longitudinalmember 1 must fulfill certain criteria with regard to strength and withregard to stiffness, but at the same time, in the interests ofminimizing weight, is to have as small a sheet thickness as possible.The individual parts 2, 2′ are therefore made of a high-tensile steelwhich, even in the case of small sheet thicknesses, has a comparativelyhigh strength combined with good formability. The stiffness losses inthe longitudinal member 1 which occur as a result of the small sheetthickness are compensated for by local stiffness-increasing deformationstructures 3 which are embossed in selected regions of the individualparts 2 by means of a deep-drawing method.

[0018] Especially high stiffness requirements are imposed on theindividual parts 2 at those regions 4 which are subjected to especiallyhigh compressive and torsional loads during operation, especially in theevent of an accident. In the present example of the longitudinallongitudinal member 1, this concerns in particular the center region 5,in which the longitudinal member 1 is of S-shaped configuration and inwhich an attachment 2″ is fastened, this attachment 2″ serving for thefastening of a cross member (not shown in FIG. 1). As indicated byarrows in FIG. 1, the main loading direction lies along the longitudinalaxes of the longitudinal-member regions 6 which adjoin the center region5. On account of the S-structure, the center region 5 is especiallysusceptible to lateral buckling under such loads, this buckling directlyresulting in displacement or twisting of the cross member.

[0019] In order to suppress the occurrence of lateral buckling in thecenter region 5 of the longitudinal member 1, the side sheet 2′ isprovided in the center region 5 with a stiffness-increasing deformationstructure 3. The hexagonal structure 3′ used in this applicationconsists of a hexagonal grid of concave bulges 7, the hollows of whichare provided with convex opposing bulges 8, so that the structure 3′, asshown in FIG. 2 in a sectional view, is formed from a grid of concaveand convex bulges 7, 8 nested one inside the other. The depth 9 of thebulges 7 and the height 10 of the opposing bulges 8 vary over the centerregion 5, so that the depth 9 of the bulges 7 and the height 10 of theopposing bulges 8 in the center 11 of the center region 5 are greaterthan in the marginal zones 12 of the center region 5. As a result, agreater stiffness increase is achieved in the center 11 (especiallysensitive to buckling) of the center region 5 than in the marginal zones12 (not so sensitive to buckling), so that the side sheet 2′ in theentire center region 5 sets up a compensating resistance to adeformation force which acts on the longitudinal member 1 from theoutside. The stiffness-increasing deformation structure 3′ is orientedto the side sheet 2′ in such a way that the direction of the maximumcompressive stiffness lies approximately perpendicularly to the bucklingdirection 13 to be expected.

[0020] The local stiffness increase, which is produced in a selectedregion 4 by the hexagonal structure 3′, depends on the depth 9 and theradius 14 of the bulges 7, on the height 10 and the radius 15 of theopposing bulges 8, and on the base length 16 of the hexagonal grid;furthermore, the local stiffness increase is not isotropic, but ratherdepends on the orientation of the grid relative to the direction of theintroduction of force, which is identified by the arrows in the exampleof the longitudinal member 1 in FIG. 1. In order to obtain a stiffeningdeformation structure 3 optimized for a particular application, theabovementioned parameters have to be matched to this application. Tothis end, a simulation of the relevant individual part 2 (or of thecomponent composed of the individual parts) and of the stiffeningstructure 3 is carried out, and the parameter setting is varied untilthe desired stiffness of selected regions 4 or the desired bucklingbehavior of the entire component is achieved.

[0021] In principle, the stiffening structure 3 may have any desiredgrid structure and symmetry. However, in order to permit a quick andreliable simulation of the component stiffness thus achieved (andtherefore to permit optimization of the component under load), it isfavorable to select a grid which has translational and rotationalsymmetry and which can be characterized by a few parameters. In additionto the hexagonal grid shown in FIGS. 1 and 2, in particularquadrilateral and triangular structures are especially suitable for thispurpose. Whereas no interplay between larger and smaller grid cells ispossible when using hexagonal grids, grid cells 17 of different size canbe combined in particular rectangular grid structures, as shown in FIG.3, so that differentiated adaptation of the local stiffness of therelevant regions is possible in this case.

[0022] The individual parts 2, the stiffness of which are to be locallyincreased in a specific manner by means of deformation structures 3, areoften parts of structural components and therefore—depending on thefunction of the component—have sheet thicknesses up to several mm. Inorder to provide such thick sheets with the complex deformationstructures 3′ shown in FIG. 1, a method which exerts high deformationforces on the sheet must be applied. To this end, it is especiallyfavorable to incorporate the deformation structures 3 as part of adeep-drawing process, while the entire component geometry is shaped froma crude sheet 18. The production of the deformation structures 3 thenrequires no separate process step, but rather it is effected as part ofthe (single-stage or multi-stage) forming of the crude sheet 18.

[0023]FIG. 4 shows a diagrammatic sketch of a deep-drawing tool 19 forthe production of the side sheet 2′ in FIG. 1. The deep-drawing tool 19comprises a punch 20 and a die 21, which are both provided with localsurface structures 22, 23 which correspond to the deformation structure3′ to be shaped on the crude sheet 18. When the punch 20 is lowered,first of all flanges 25, 25′ are bent on the crude sheet 18 by theaction of edge regions 24, 24′ on punch 20 and die 21, additional sheetsbeing welded at these flanges 25, 25′ to the side part 2′ in a laterprocess step. When the punch 20 is lowered further, the deformationstructure 3 is then also produced on the crude sheet 18; this is done atthe final pressure of the deep-drawing punch 20. Suitable control of thepressure forces of the hold-downs 26 during the lowering of the punch 20ensures that, during the shaping of both the flanges 25, 25′ and thedeformation structure 3, sufficient material can flow out of the sideregions 27 of the crude sheet 18 into the inner regions 28 to be shapedand thus cracks or folds of the crude sheet 18 cannot occur either inthe region of the flanges 25, 25′ or on the stiffness-increasingdeformation structures 3.

[0024] From case to case, depending on the geometry of the individualpart 2 to be shaped, those punch and die regions 22, 23 which shape thestiffness-increasing deformation structure 3 are subjected to higherwear during the deep-drawing process than the rest of the tool; it istherefore advisable from case to case to strengthen these regions 22, 23of the punch 20 and the die 21, respectively, by tool inserts 29, 30made of an especially hard or resistant material.

[0025] The method according to the invention can be used for the localstiffness increase of plate-shaped workpieces 1 of different thicknesswhich may be made from a wide range of different (deformable) materials.The stiffness-increasing structures 3 can be used for strengthening anyregions which are subjected to particular compressive and/or torsionalloads. Furthermore, weak points can be specifically provided in thecomponent 1 by means of such a local deformation structure 3, at whichweak points the component, in the event of a certain load, buckles orbreaks. In addition to the above-described deformation structure 3 ofconcave bulges 7 and convex bulges 8 nested one inside the other, thegrid cells 17 may also have a more complex convex/concave form if, forexample, each concave bulge 7 is provided in its interior with a convexopposing bulge 8 which in turn has a convex bulge in its center.

1. A component consisting of a high-strength sheet which is providedwith a stiffness-increasing deformation structure in a defined, locallylimited stiffening region which is especially important for thedimensional stability of this component, characterized in that thedeformation structure (3) consists of a periodic grid of adjacent cells(17), each grid cell (17) containing concave and convex bulges (7, 8)nested one inside the other.
 2. The component as claimed in claim 1,characterized in that the deformation structure (3) has a hexagonalstructure.
 3. A method of producing a locally limited,stiffness-increasing deformation structure on a component whose geometryis shaped from a sheet-metal billet of high dimensional stability bymeans of a drawing method, characterized in that the deformationstructure (3), consisting of a periodic grid of concave and convexbulges (7, 8) nested one inside the other, is produced on the componentby means of a drawing method.
 4. The method as claimed in claim 3,characterized in that the deformation structure (3) is shaped togetherwith the component geometry in the same process step.